Concussions, affecting 1.6 - 3.8 million Americans annually, can pose potentially serious consequences including second impact syndrome, with a 50% mortality rate, in the short term and elevated risk of chronic traumatic encephalopathy, amyotrophic lateral sclerosis, mild cognitive impairment, clinically diagnosed depression, and a potentially earlier onset of Alzheimer disease in the long term. While current assessment techniques for identifying the presence of a concussion has made substantial progress in recent years, the assessment protocols are typically not useful in making return to participation decisions due, in large part, to practice effects and low sensitivity to subtle impairments. Specifically, postural control is assessed utilizing the Balance Error Scoring System (BESS), however this test is has low inter- and intra-rater reliability and is subject to a practice effect. Therefore, a pressing need exists to develop an objective method to identify critical subtle, lingering impairments in postural control following a concussion and to develop a practical method of ongoing assessment for clinicians. Biomechanical assessment of gait initiation (GI), gait, and gait termination (GT) provides an objective method of identifying postural instabilities in a wide range of balance impaired groups. Further, the addition a secondary cognitive task challenges the limited functional reserves of the individual post-concussion. Therefore, the general hypothesis of this proposal is that single and dual-task GI, gait, and GT will individually and collectively identify impairments in postural stability following a concussion and these impairments will persist after the individual has returned to baseline on traditional clinical measures of concussion recovery;symptom resolution, BESS, and neuropsychological performance. Our hypothesis will be tested by 2 specific aims: 1) determine if impairments in postural stability following a concussion can be identified through single and dual task GI, gait, and GT, and 2) to compare the performance of G, gait, and GT to internationally recommended protocols to assess recovery. Thirty-six subjects with acute concussions will be tested daily from the day after their concussion until they return to participation and will be matched with thirty- six non-concussed subjects. The primary outcome measures;center of pressure displacements and velocity, spatiotemporal parameters of locomotion, and ground reaction forces will be compared both within and between subjects utilizing survival analysis. We hypothesize, supported by our preliminary data, that GI, gait, and GT will identify impairments in postural stability and these impairments will persist beyond return to baseline of the BESS assessment. These findings, if objectively documented, would demonstrate that current clinical assessments of postural stability are insufficient and will provide a new, clinically practical method of identifying persistent impairments in dynamic postural stability following a concussion. PUBLIC HEALTH RELEVANCE: Premature return to participation following a concussion leads to elevated risk of both repeat concussions and the potential for long term risk of brain damage;thus, accurate and timely concussion assessment and reassessment is a vital component of making medically correct decisions on return to participation. This project aims to improve the current standards of ongoing concussion assessment by identifying lingering and persistent subtle impairments in postural control and thus providing clinicians with an additional set of tools to assist in ongoing recovery assessment. The results of this project support the NIH's stated mission of extending the healthy life by potentially reducing premature return to participation and therefore limiting the risks of the potentially fatal second impact syndrome as well as repeat concussions and their associated life-long consequences.